Hydrogen is a “clean fuel” because it can be reacted with oxygen in hydrogen-consuming devices, such as a fuel cell or combustion engine, to produce energy and water. Virtually no other reaction byproducts are produced in the exhaust. As a result, the use of hydrogen as a fuel may solve many environmental problems associated with the use of petroleum based fuels. Cost-effective, safe and efficient storage of hydrogen gas is important for many applications that use hydrogen. In particular, minimizing the volume and weight of hydrogen storage systems is important in mobile applications.
Several methods of storing hydrogen currently exist but are either inadequate or impractical for consumer applications. For example, hydrogen can be stored in liquid form at very low temperature or hydrogen can be stored under high pressure in cylinders, however, both of such storage methods are not practical for most consumer applications for a number of well known reasons related, for example, to safety and economics. Other methods of hydrogen storage include the use of chemical compounds that either: (a) chemically react with water or other species to generate hydrogen; or (b) reversibly adsorb and then release hydrogen. However, these methods are also not practical for most consumer applications for a number of well known reasons related, for example, to safety and economics.
U.S. Pat. No. 6,534,033 issued Mar. 18, 2003, discloses a hydrogen generation system that includes a stabilized metal hydride solution and a hydrogen generation catalyst system which includes a supported hydrogen generation catalyst having molecules of a hydrogen generation catalyst bound to, entrapped within, and/or coated onto a substrate. In one disclosed system, mechanical pumps pump a sodium borohydride solution through a catalyst chamber containing precious metal catalysts. One disadvantage of such a system is that mechanical pumps are not only unreliable and heavy, but tend to leak and/or clog in the presence of the highly caustic solutions used. This reduces the reliability of the device. In addition, precious metal catalysts tend to wash out of the catalyst chamber due to the abrasive nature of the solution. This loss of precious metal catalyst is not only expensive but also results in seriously reduced catalytic activity and reduced hydrogen output. In further addition, the catalyst chamber must be periodically replaced.
U.S. Patent Application No. 2004/0009392 A1, published on Jan. 15, 2004, (the “'392 Application”), discloses a compact and efficient hydrogen generator operating on the electro-galvanic principle in which hydrogen is generated by establishing an electrical connection between a cathode material and an anode material that is at least partially submerged in a stabilized metal borohydride electrolyte solution, wherein the cathode material forms at least part of the inner surface of the electrolyte container. '392 Application FIGS. 1 and 1A. Further embodiments provided in the '392 Application include the use of an anode fabricated from many types of anode material ('392 Application FIG. 3); the use of internal and external water storage and release into the electrolyte to replenish water consumed during hydrogen production ('392 Application FIGS. 4-6); the use of multiple anodes fabricated from the same anode material and an electrolyte storage and release tank made of different materials ('392 Application FIG. 7); and the implementation of a mechanism for raising or lowering the anodes from or into the electrolyte solution ('392 Application FIG. 8). The teachings of the '392 Application are incorporated herein by reference into the present application.